Choosing a subwoofer

2017-10-13 03:29:10

Searches back to 2003 didn't yield anything general enough, so here goes...

I'm getting ready to buy a subwoofer for my stereo system; it is to be used for music only, no HT. There (not surprisingly) seems to be very little guidance in the many A/V forums on how to choose an appropriate unit. Most people seem to want wall-breaking volume and are very vague on LF requirements, and discussions usually diverge until the posters are talking about $6000 subs which require their own sub(station) for power. Or the wackos come in and start talking about "musical" and "fast" subs and all useful discussion ends.

Here's the environment. My Magneplanar 1C system is currently at Magnepan for refurb, and it will be the main speaker. I'm planning to do as I did before, bi-amp + subwoofer. I have adequate power in terms of a couple of Dynaco 400s (or a 150 which I used on the tweeter panels before). The room is 10x24x7 (1700 ft^3) and carpeted, with a number of bookcases breaking up the modes a little and a rear wall that is mostly stairs. I accept that I may need some room treatment once I get things situated, as well as some repositioning of all the speakers. I have REW and a calibrated measurement mic as well as some experience in doing room evaluation.

What I'm trying to achieve is LF extension that will allow me to play organ music and the occasional rock synthesizer at a level which will keep up with the Maggies. I really don't foresee playing anything as loud as 90dB except maybe the occasional peaks; I just want depth, not demolition. That said, I do have a number of recordings which feature useful content in the 20-30Hz range and I know the Fletcher-Munson curves say that the lows will need to be much louder to be perceived as such. I had a M&K Volkswoofer installed before (it was cheap!), and despite trying everything to reposition and adjust it, I never got a satisfying LF response. I recently re-foamed the driver and sealed some possible cab leaks but it still doesn't seem to go very low. I suspect there are far better drivers and systems available today anyway.

Just as a point of reference, I have a cheap Polk sub sitting under my office desk - which means I'm benefiting from proximity in this much smaller room - and it measures and sounds reasonably flat down to about 30 Hz from this one listening position. I know it (or its bigger brothers) wouldn't work in the larger room, but tweaking it has satisfied me that I do want that extended low end and that it benefits me with enough music that I want to pursue it.

I know there will be some room gain in the room with my main system, but how much? Will one premium subwoofer actually be able to handle the load? I really can't justify spending $2000 for the sub unless I'm convinced it will provide a real tangible improvement over an $800 sub. I'm willing to invest in a kit if one exists, to save some outlay; electronics and woodworking don't scare me off. Am I even asking the right questions? Do I want something that's not achievable at a reasonable price?

Re: Choosing a subwoofer

This is a tough one... And, I'm sure you know that organ music... realistic organ music... is not easy to reproduce!

The best thing would be to find a good home theater/hi-fi shop that will allow you to try-out a sub or two at home before buying. As you know, room acoustics make a big difference, especially in the low-end. Plus, odds are the showroom won't have Magneplanars to pair-up with.

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I'm planning to do as I did before, bi-amp + subwoofer. I have adequate power in terms of a couple of Dynaco 400s (or a 150 which I used on the tweeter panels before).

You can do that, but most modern subs are active/powered because most home theater receivers only have line-out for the sub. I assume you have an active crossover?

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The room is 10x24x7 (1700 ft^3) and carpeted, with a number of bookcases breaking up the modes a little and a rear wall that is mostly stairs.

The carpet & bookcases won't have much affect on the bass (because of the long wavelengths). It's hard to say what the stairs are doing to the sound.

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I accept that I may need some room treatment once I get things situated, as well as some repositioning of all the speakers. I have REW and a calibrated measurement mic as well as some experience in doing room evaluation.

That's good... It's always best to measure/diagnose before you treat. For the low-end, treatment would probably mean bass traps (and possibly re-positioning the sub). Note that bass traps trap the bass that would otherwise be reflected, so trapping the bass can boost frequencies that would otherwise be canceled as well as knock-down the frequencies that would otherwise be reinforced.

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I'm willing to invest in a kit if one exists, to save some outlay;

Parts Express sells a couple of subwoofer kits, or they have a selection of cabinets, drivers, plate-amplifiers, crossovers, etc. If you are choosing your own driver & choosing/building your own cabinet, there is software to help predict performance/frequency response (WinISD is free).

I built my own subs, but of course the problem is you don't really know what you're getting 'til your done (although you can[ adjust the port or reduce the effective enclosure volume). And, you can't return a kit or home-built speaker.

Re: Choosing a subwoofer

This is a tough one... And, I'm sure you know that organ music... realistic organ music... is not easy to reproduce!

The best thing would be to find a good home theater/hi-fi shop that will allow you to try-out a sub or two at home before buying. As you know, room acoustics make a big difference, especially in the low-end. Plus, odds are the showroom won't have Magneplanars to pair-up with.

Oh yes - it's a challenge for sure. I'll accept that I won't be able to produce it at full theater volume.

There's one dealer in the state which has the (small, modern) Maggies. Unfortunately, they pretty much only have Klipsch subs and they're all wired into the HT room. I'll admit to a slight prejudice against Klipsch based on the speakers I heard during the 70s and 80s, but if their subs are a decent value I might talk to this place about a loaner.

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I'm planning to do as I did before, bi-amp + subwoofer. I have adequate power in terms of a couple of Dynaco 400s (or a 150 which I used on the tweeter panels before).

You can do that, but most modern subs are active/powered because most home theater receivers only have line-out for the sub. I assume you have an active crossover?

Right; I was just giving a reference for how much power is available to drive the mains. I fully expect to use a powered sub, and when I designed my active crossover it was with that sort of use in mind. I have a mono/stereo sub out from the crossover.

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That's good... It's always best to measure/diagnose before you treat. For the low-end, treatment would probably mean bass traps (and possibly re-positioning the sub). Note that bass traps trap the bass that would otherwise be reflected, so trapping the bass can boost frequencies that would otherwise be canceled as well as knock-down the frequencies that would otherwise be reinforced.

Understood, and I'm prepared to spend some time and money dealing with this!

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I'm willing to invest in a kit if one exists, to save some outlay;

Parts Express sells a couple of subwoofer kits, or they have a selection of cabinets, drivers, plate-amplifiers, crossovers, etc. If you are choosing your own driver & choosing/building your own cabinet, there is software to help predict performance/frequency response (WinISD is free).

I built my own subs, but of course the problem is you don't really know what you're getting 'til your done (although you can[ adjust the port or reduce the effective enclosure volume). And, you can't return a kit or home-built speaker.

For good or ill, I can't use WinISD (Mac) but that's OK - I'm saving "design and build" as a last resort. I am aware of the PE sub kits, and also have seen the AV/HT crowd sneer at the Dayton subs. But honestly they look well made and seem to have a plausible LF response which intrigues me. I've looked for reviews of the Dayton RS1202 or Ultimax but what I've seen is either from people who are focused on LFE instead of music, or "audiophiles" who like their high-end brands. I know PE has a no-hassle return policy on their prebuilt systems but not, of course, on their kits. Maybe someone with direct knowledge of their subs will check in here...

Re: Choosing a subwoofer

I really can't justify spending $2000 for the sub unless I'm convinced it will provide a real tangible improvement over an $800 sub. I'm willing to invest in a kit if one exists, to save some outlay; electronics and woodworking don't scare me off.

Re: Choosing a subwoofer

Re: Choosing a subwoofer

I am aware of the PE sub kits, and also have seen the AV/HT crowd sneer at the Dayton subs.

Zero snob-appeal...

I don't know anything about them, but I'm pretty sure either one would be adequate for me (rock music). I'm just not sure about those clean-low organ notes... It looks like adequate cone area and plenty of power, so as long as it's not a bad cabinet design, I assume it's good enough for rock music (or movies). The cabinets do look a little small to me.

Re: Choosing a subwoofer

Thanks, Arny. I discovered that site a few days ago and it was partly what led me to the Dayton sub kits.

The Rhythmik kits look very interesting and are inexpensive in terms of parts. This begins to look appealing, as building a box is not such a big deal. Time-consuming, I guess, but that's fine.

The only SVS cylinder that comes in even close to the same price is their 12" - would a single cylinder be able to compete with a single Ultimax or Rhythmik 15 CI? Even with the modern high Xmax drivers, I'm a little dubious about 12" speakers for extreme lows at realistic volume.

Re: Choosing a subwoofer

I am aware of the PE sub kits, and also have seen the AV/HT crowd sneer at the Dayton subs.

Zero snob-appeal...

I don't know anything about them, but I'm pretty sure either one would be adequate for me (rock music). I'm just not sure about those clean-low organ notes... It looks like adequate cone area and plenty of power, so as long as it's not a bad cabinet design, I assume it's good enough for rock music (or movies). The cabinets do look a little small to me.

I'm totally OK with the zero snob appeal. No one else is going to be hearing this system except occasionally friends who care even less than I do.

It says the Ultimax 18 is 4 ft^3 which is in line with their recommendations for the UM18-22 driver, FWIW - and of course it's going to be stuffed with fiber which makes the box look larger by as much as 40%. Data-bass puts the output at 16 Hz in the same league as the more expensive Hsu, Rhythmik and SVS boxes, so it is probably as good as I'm going to get without spending an astronomic amount.

Re: Choosing a subwoofer

Parts Express sells a couple of subwoofer kits, or they have a selection of cabinets, drivers, plate-amplifiers, crossovers, etc. If you are choosing your own driver & choosing/building your own cabinet, there is software to help predict performance/frequency response (WinISD is free).

Sad to find that virtually all of the Dayton subwoofer kits have been discontinued. I guess I won't be building a second 15" Titanic sub any time soon.

Re: Choosing a subwoofer

The Rhythmik kits look very interesting and are inexpensive in terms of parts. This begins to look appealing, as building a box is not such a big deal.

Of course the Rythmiks aren't boxes. They are dipoles, like the Maggies. 6db less power into the modal decay of the room. No bass traps and such idiocy. All explained in the paper. The Maggies will run out of steam way before they do.

Re: Choosing a subwoofer

The Rhythmik kits look very interesting and are inexpensive in terms of parts. This begins to look appealing, as building a box is not such a big deal.

Of course the Rythmiks aren't boxes. They are dipoles, like the Maggies. 6db less power into the modal decay of the room. No bass traps and such idiocy. All explained in the paper. The Maggies will run out of steam way before they do.

Re: Choosing a subwoofer

I really can't justify spending $2000 for the sub unless I'm convinced it will provide a real tangible improvement over an $800 sub. I'm willing to invest in a kit if one exists, to save some outlay; electronics and woodworking don't scare me off.

Re: Choosing a subwoofer

3.3 Is the perception of spatial informationin a recording affected by the decay timeof room modes in the listening room?This question is largely answered by the paperssummarised in section 2. Papers describing tests whichfound little or no spatial effect at low frequencies[31][32][33] were all done in listening rooms with longdecay times at low frequencies. Papers which describetests showing detection of spatial information at lowfrequencies [37][38][39] were done in rooms withlower decay times. [39] used two rooms with differentdecay times and found that discrimination wasnoticeably easier in the room with lower decay time.[25] and [41] point out that it is easier to hear in to therecording when the modal artifacts in the listeningroom do not dominate.

Re: Choosing a subwoofer

I think he's saying the H-baffle plus a pair of woofers and the amp listed in the link constitute a dipole woofer. I can't read the paper because I'm not an AES member.

I am an AES member, and I just refreshed my memory of the paper. There are no plans of actual speakers in it, and the paper only mentions dipoles twice, in the general context of a laundry list of speaker types. For example:

"The motivation for their studieswas the difference in coupling to the room dependingon whether the source is more a pressure source(monopole) or a pressure-gradient source (dipole) orsomewhere in between (cardioid). Comparison of asingle monopole with a single cardioid (at the sameposition) showed that the cardioid produced shorterdecay times than the monopole. Use of multiplecardioids showed a further reduction in the decay time,and showed less variation in response at differentlistening positions. "

The above follows from the directivity or Q of the respective speaker system types. Of the bunch, cardioid subwoofers have become popular in large venues, which is arguably a whole different kind of audio reproduction than home audio., starting with the important difference in Schroeder frequencies of the rooms.

The abstract of the paper is acessible to anybody for free and says:

"This paper reviews literature related to the reproduction of bass in small rooms. The overall picture givenby this review shows weaknesses in the current recommendation of using a single subwoofer to playfrequencies below 80 to 120Hz.Results of listening tests related to room modes and spatial information are summarised. Three techniquesfor reducing the problem of room modes are described: i) modal equalisation, ii) the use of a mono basssignal from multiple subwoofers to give a more even response throughout the listening area and iii) the useof subwoofers with cardioid or dipole polar response. To improve the presentation of spatial informationthe use of stereo bass is considered.The question as to whether it is possible to achieve the best of controlling room modes and presentingspatial information is still open. "

Its conclusion is as inconclusive and non-decisive as the abstract might suggest:

"The standard 5.1 configuration has two fundamentalweaknesses at low frequencies: a) no opportunity totransmit low frequency spatial information present in arecording, and b) limited opportunity to control roommodes. Some control of room modes can be achievedby experimenting with location in the room or bymodal equalisation.Use of a mono signal, replayed via multiplesubwoofers with suitable signal processing, allows oneto present more uniform bass over a listening area.However there is still no opportunity to present spatialinformation.Use of two subwoofers placed to the left and right ofthe listener and playing left and right LF signals allowspresentation of spatial information.The system which has been studied least in theliterature is the one where all 5 (or 7) main channel loudspeakers have good low frequency response. Thissystem in combination with appropriate signalprocessing would seem to present the greatestopportunity for controlling room modes, using bothmodal equalisation and the interaction of multiple driveunits, and presenting spatial information. "

Bipolar systems are a double pain in the @$$ because they are less directive than the rest, and most designs oriented that way have far poorer bass dynamic range, as well as a well-deserved reputation for difficulty in finding rooms and places in rooms where they can work advantageously "

So in the end, the cited paper is about the justification for stereo bass. While the use of two independently placed and equalized subwoofers has some general applicability and recognized success for obtaining a more uniform bass sound field in a listening room, the world does not seem to be beating a path to the door of stereo bass.

That rooms with long RT's at low frequencies are adverse to the perception of audible differences related to multichannel bass may or may not actually mean anything. What are the requirements for good transient performance at very low frequencies? AFAIK, that has not been a hot topic for recent acoustic research.

I would think that efforts that improve the uniformity of the bass sound field might also be advantageous for the perception of multichannel bass.